Implement flatTap #651
Implement flatTap #651
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lib/index.js
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| @@ -2167,6 +2167,28 @@ addMethod('doto', function (f) { | |||
| Stream.prototype.tap = Stream.prototype.doto; | |||
| _.tap = _.doto; | |||
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| /** | |||
| * Applies a function to each value from the source, and re-emits the | |||
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Can you mention that
- The function must return a Highland stream.
- The source value will not be re-emitted until the stream that the function returns ends.
lib/index.js
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| * @param {Function} f - the function to apply | ||
| * @api public | ||
| * | ||
| * _([1, 2, 3]).flatTap(httpLog) |
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Can you add an example for how httpLog would need to be implemented? Maybe using promises + setTimeout + console.log to illustrates the fact that the stream will wait until the stream completes before it continues..
lib/index.js
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| addMethod('flatTap', function (f) { | ||
| return this.flatMap(function (x) { | ||
| return f(x) | ||
| .flatMap(function () { |
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I know I mentioned that flatTap could be implemented with flatMap like this, but a complete implementation should account for the fact that the stream f(x) may emit zero values or more than one values. You're better off implementing with consume and looking for the _.nil sentinel instead.
test/test.js
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| @@ -4909,6 +4909,86 @@ exports['tap - doto alias'] = function (test) { | |||
| test.done(); | |||
| }; | |||
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| exports.flatTap = function (test) { | |||
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Can you implement the tests using the object syntax (see the tests for pull as an example). This will group them together into a suite that makes it easier to run separately.
test/test.js
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| var seen; | ||
| function record(x) { | ||
| var y = x * 2; | ||
| seen.push(y); |
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seen.push(y) should be done asynchronously. You want to verify that the stream actually waits until the completion of the async action before continuing.
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Oh, I see you do this in the GeneratorStream and ArrayStream tests. You can just remove this test then, since it doesn't seem to add any value.
test/test.js
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| var f = function (x) { | ||
| return _(function (push, next) { | ||
| setTimeout(function () { | ||
| push(null, x * 2); |
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Can you verify that this code executes before toArray completes? The seen.push(y) approach that you use above is fine.
Also do this for the GeneratorStream test.
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Hi @tomwhale, Sorry for dropping the ball on this. I made some comments when you first sent this PR, but got confused by Github's interface and never ended up posting them. |
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Sorry, had a chance to pick this up again. I think I have resolved all your comments. If I have misunderstood what you meant, lemme know! |
lib/index.js
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| * @param {Function} f - the function to apply | ||
| * @api public | ||
| * | ||
| * const httpLog = H(new Promnise(res => { |
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Use _ instead of H for the Highland object.
| * const httpLog = H(new Promnise(res => { | |
| * const httpLog = _(new Promnise(res => { |
lib/index.js
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| return this.flatMap(function (x) { | ||
| return f(x).consume(function (err, y, push, next) { | ||
| if (err) { | ||
| // next(); |
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I think you should push the err in this case and continue on with the stream. That's what most transforms do. The user can use stopOnError if they want to stop the stream early.
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Okay, this is an interesting one though, as it is a tap you could argue the error should be silenced? I think I do agree with you though.
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There's definitely a lot of uses of tap where you want to ignore errors. I just don't like unilaterally silencing errors in library functions. That's something that developer using the library should decide.
Also, your fix isn't entirely correct. It pushes nil immediately after an error. In general, Highland streams don't end after the first error, so you need to call next instead of push(null, _.nil).
| s.pull(valueEquals(test, 3)); | ||
| test.done(); | ||
| }, | ||
| 'flatTap - argument function throws': function (test) { |
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Can you add a similar test to this, but for the stream (i.e., the return value of the argument function) emitting an error instead.
Something like this,
_([1, 2, 3, 4]).flatTap((x) => _((push) => {
push(err);
push(null, _.nil);
}));
From Issue #616
This method creates a short hand for the following:
stream.flatMap(item => save(item).map(_ => item))where save returns a highland stream.